1. Field of the Invention
The present invention relates to a two-way valve having a first port and a second port for introducing or discharging a pressure fluid in two directions.
2. Description of the Related Art
A two-way valve has been conventionally used for a fluid pressure circuit or the like. A conventional two-way valve of the above type is shown in FIG. 5 (see, for example, U.S. Pat. No. 5,131,627). The two-way valve 1 has a first port 2 and a second port 3 for introducing or discharging a pressure fluid. A piston 5 is displaceable under the action of a pilot pressure supplied via a pilot port 4. A communicating passage 7 providing communication between the first port 2 and the second port 3 is opened or closed by a diaphragm (valve plug) 6 operated integrally with the piston 5.
According to the conventional two-way valve 1, however, the flow rate of the pressure fluid discharged from the second port 3 via the communicating passage 7 is previously fixed by the valve opening degree of the diaphragm 6 to function as the valve plug, i.e., the displacement amount of the piston 5 displaceable under the action of the pilot pressure. The flow rate of the pressure fluid discharged from the second port cannot be changed at multiple stages in the two-way valve 1.
If a certain fluid is charged into an unillustrated vessel, the pressure fluid is charged at a large flow rate per unit time at the initial stage. Then, the pressure fluid is charged into the vessel at a predetermined flow rate after the flow rate of the pressure fluid is changed to a minute flow rate per unit time at the intermediate stage or at the final stage. Then, it is impossible for the conventional two-way valve to freely change the flow rate of the pressure fluid charged within unit time because the flow rate of the pressure fluid charged within unit time is fixed to a constant value.
It is assumed that a flow rate control valve (not shown) for controlling the flow rate of the pressure fluid charged into the vessel is disposed between the vessel and the conventional two-way valve. However, it is necessary to use a member such as the flow rate control valve in addition to the two-way valve. The tubing operation of the above system is complicated and the cost of purchasing the flow rate control valve is increased.
It is a general object of the present invention to provide a two-way valve which makes it possible to change a flow rate of a pressure fluid to be discharged within unit time at multiple stages by using a simple structure.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.